JP2015044145A - Honeycomb catalyst and exhaust gas purification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a honeycomb catalyst which is excellent in NOx purification performance and is capable of suppressing breakage of a honeycomb unit during the use of an exhaust gas purification device.SOLUTION: There is provided a honeycomb catalyst having a honeycomb unit in which a plurality of through-holes are provided side by side in a longitudinal direction while being separated by partition walls, wherein the honeycomb unit includes first zeolite, second zeolite and an inorganic binder, the first zeolite is an aluminosilicate having a CHA structure and the composition ratio Si/Al is 15 to 50, the second zeolite is a silicoaluminophosphate and the composition ratio Si/(Si+Al+P) is 0.1 to 0.25 and the volume ratio between the first zeolite and the second zeolite (the first zeolite:the second zeolite) is 75:25 to 90:10.

Description

The present invention relates to a honeycomb catalyst and an exhaust gas purification device.

2. Description of the Related Art Conventionally, an SCR (Selective Catalytic Reduction) system that uses ammonia to reduce NOx to nitrogen and water is known as one of systems for purifying automobile exhaust gas.

Further, a catalyst carrier used in the SCR system is known in which a composition containing zeolite is formed into a honeycomb shape.

For example, in Patent Document 1, the honeycomb unit includes a first zeolite, a second zeolite, and an inorganic binder, and the first zeolite is a β-type zeolite and / or a ZSM-5-type zeolite, A honeycomb structure in which the zeolite is a phosphate zeolite such as SAPO is disclosed. In the honeycomb structure described in Patent Document 1, since the first zeolite such as β-type zeolite is present around the second zeolite such as SAPO, the second zeolite adsorbs or desorbs water, and the honeycomb Mitigating the expansion or contraction of the unit.

On the other hand, Patent Document 2 discloses a zeolite having a CHA structure ion-exchanged with copper ions as a zeolite catalyst used in an SCR system. The zeolite catalyst described in Patent Document 2 is considered to have high NOx purification performance after aging (aging) with hot water.

International Publication No. 2011/061835 US Pat. No. 7,601,662

In order to obtain a honeycomb catalyst excellent in NOx purification performance, the present inventors have prepared a honeycomb containing a composition containing a zeolite having a CHA structure as described in Patent Document 2 (hereinafter also referred to as CHA-type zeolite). It was considered to form into a shape.

However, when a honeycomb catalyst is produced using a honeycomb unit containing CHA-type zeolite and an exhaust gas purification device equipped with the honeycomb catalyst is mounted on a vehicle, the honeycomb unit is cracked during use, and the honeycomb unit is damaged. It turns out that a problem arises.

The present invention has been made in order to solve the above-described problem, and provides a honeycomb catalyst and an exhaust gas purification device that are excellent in NOx purification performance and can suppress damage to the honeycomb unit during use of the exhaust gas purification device. The purpose is to provide.

The present inventors have examined the cause of the honeycomb unit being damaged during the use of the exhaust gas purification apparatus. As a result, the present inventors have found that the honeycomb unit is damaged by expansion of the CHA-type zeolite particles due to water absorption and capillary stress when water enters the pores of the honeycomb unit.

Based on such examination results, the present inventors have sufficient NOx purification performance by mixing CHA and SAPO to form a honeycomb unit, and while using the exhaust gas purification device. The present inventors have found that a honeycomb unit that is not easily damaged can be obtained.

That is, the honeycomb catalyst of the present invention is a honeycomb catalyst including a honeycomb unit in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls therebetween, and the honeycomb unit includes the first zeolite and the second zeolite. And the first zeolite is an aluminosilicate having a CHA structure, the composition ratio Si / Al is 15 to 50, and the second zeolite is a silicoaluminophosphate, The composition ratio Si / (Si + Al + P) is 0.1-0.25, and the volume ratio of the first zeolite and the second zeolite (first zeolite: second zeolite) is 75:25. 90:10.

In the honeycomb catalyst of the present invention, it is possible to improve the NOx purification performance by using a honeycomb unit having a main raw material of an aluminosilicate having a CHA structure (hereinafter also referred to as CHA) which is the first zeolite. it can. Further, by mixing CHA and silicoaluminophosphate (hereinafter also referred to as SAPO), which is the second zeolite, to form a honeycomb unit, the entire honeycomb unit is relieved of water absorption and dehydration stress. be able to. When the volume ratio of CHA exceeds 90, the honeycomb unit may be damaged due to absorption / dehydration displacement, and since the thermal expansion coefficient of CHA is −4.5 × 10 ⁻⁶ / K or less, The unit may be damaged. When the volume ratio of CHA is less than 75, the amount of SAPO is relatively large, and the honeycomb unit may be similarly damaged due to the stress caused by shrinkage during water absorption and expansion during dehydration.

Based on the above, by setting the volume ratio of CHA and SAPO to 75:25 to 90:10, the NOx purification performance is excellent, and the honeycomb unit is damaged during use of the exhaust gas purification device (damage due to water absorption / dehydration and thermal stress). ) Can be suppressed.

The average particle size of the first zeolite is preferably 0.1 to 2.0 μm. When the average particle size of the first zeolite is 0.1 to 2.0 μm, the pore size of the honeycomb unit can be increased, the capillary stress during water absorption is reduced, and further the NOx purification performance is improved by gas diffusion. Is possible.

The average particle size of the second zeolite is preferably 1/5 to 50 times the average particle size of the first zeolite. It becomes possible to adjust the pore diameter of the honeycomb unit.

The first zeolite and / or the second zeolite are preferably ion-exchanged with copper ions. The NOx purification performance can be improved.

The honeycomb unit preferably contains the copper ions in an amount of 5.5 to 7.5 g / L per apparent volume of the honeycomb unit. Since the NOx purification performance when the exhaust gas temperature is low can be increased and the decrease in the NOx purification performance due to ammonia oxidation at a high temperature can be prevented, high NOx purification performance is exhibited over the entire temperature range.

The honeycomb unit preferably contains the first zeolite at 150 to 250 g / L per apparent volume of the honeycomb unit. Since the NOx purification performance when the exhaust gas temperature is low can be increased and the decrease in the NOx purification performance due to ammonia oxidation at a high temperature can be prevented, high NOx purification performance is exhibited over the entire temperature range.

The honeycomb unit preferably further includes one or more selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances, and three-dimensional needle-like substances. The strength of the honeycomb catalyst can be improved.

Moreover, the exhaust gas purification apparatus of the present invention includes the honeycomb catalyst of the present invention.

According to the present invention, it is possible to provide a honeycomb catalyst and an exhaust gas purification device that are excellent in NOx purification performance and can suppress damage to the honeycomb unit during use of the exhaust gas purification device.

It is a perspective view which shows typically an example of the honeycomb catalyst of this invention. It is sectional drawing which shows typically an example of the exhaust gas purification apparatus of this invention. It is a perspective view which shows typically another example of the honeycomb catalyst of this invention. Fig. 4 is a perspective view schematically showing an example of a honeycomb unit constituting the honeycomb catalyst shown in Fig. 3. It is a graph which shows the change rate of the thermal expansion coefficient with respect to temperature in the honeycomb unit produced in the Example and the comparative example.

Hereinafter, the present invention will be specifically described. However, the present invention is not limited to the following description, and can be appropriately modified and applied without departing from the scope of the present invention.

The honeycomb catalyst of the present invention is a honeycomb catalyst including a honeycomb unit in which a plurality of through holes are arranged in parallel in a longitudinal direction with partition walls, and the honeycomb unit includes a first zeolite, a second zeolite, and an inorganic catalyst. The first zeolite is an aluminosilicate having a CHA structure, the composition ratio Si / Al is 15 to 50, and the second zeolite is a silicoaluminophosphate, the composition of which is The ratio Si / (Si + Al + P) is 0.1 to 0.25, and the volume ratio of the first zeolite to the second zeolite (first zeolite: second zeolite) is 75:25 to 90: 10 is a feature.

FIG. 1 shows an example of the honeycomb catalyst of the present invention. A honeycomb catalyst 10 shown in FIG. 1 includes a single honeycomb unit 11 in which a plurality of through-holes 11a are arranged in parallel in the longitudinal direction with a partition wall 11b therebetween, and an outer peripheral coating layer 12 is provided on the outer peripheral surface of the honeycomb unit 11. Is formed. The honeycomb unit 11 includes a first zeolite, a second zeolite, and an inorganic binder.

In the honeycomb catalyst of the present invention, the first zeolite contained in the honeycomb unit is an aluminosilicate (CHA) having a CHA structure. The CHA structure is a code that defines the structure of the zeolite defined by the International Zeolite Association (IZA) and indicates the CHA structure. This is a zeolite having a crystal structure equivalent to that of naturally occurring chabazite.

The CHA composition ratio Si / Al is 15 to 50, preferably 20 to 40, and more preferably 25 to 35. When the composition ratio is less than 15, Al is increased and thermal deterioration is likely to occur. On the other hand, if the composition ratio exceeds 50, the acid sites of the zeolite may decrease and the NOx purification performance may decrease.

The average particle diameter of CHA is desirably 0.1 to 2.0 μm, more desirably 0.3 to 1.8 μm, and further desirably 0.7 to 1.7 μm. When the average particle diameter of CHA is 0.1 to 2.0 μm, the pore diameter of the honeycomb unit can be increased, the capillary stress at the time of water absorption can be reduced, and further the NOx purification performance by gas diffusion can be improved. Become.
The average particle size of CHA is the average particle size of primary particles measured using a scanning electron microscope (SEM).

The specific surface area of CHA is preferably 500 to 650 m ² / g and more preferably 550 to 630 m ² / g from the viewpoint of the crystal structure.

The CHA content in the honeycomb unit is preferably 40 to 75% by volume, more preferably 45 to 70% by volume, and still more preferably 50 to 65% by volume. When the CHA content is less than 40% by volume, the NOx purification performance is lowered. On the other hand, if the CHA content exceeds 75% by volume, the honeycomb unit is likely to be damaged by absorption / dehydration or thermal stress.

In the honeycomb catalyst of the present invention, the second zeolite contained in the honeycomb unit is silicoaluminophosphate (SAPO). Zeolite is an aluminosilicate in a narrow sense, but also includes silicoaluminophosphate (SAPO) in a broad sense, and the broad sense is adopted in the present invention.

The composition ratio Si / (Si + Al + P) of SAPO is 0.1 to 0.25, preferably 0.1 to 0.23, and more preferably 0.12 to 0.20. When the composition ratio is less than 0.1, there are few copper ion exchange sites, and the NOx purification performance decreases. On the other hand, if the composition ratio exceeds 0.25, structural defects increase and NOx purification performance decreases.

Although it does not specifically limit as SAPO, SAPO-5, SAPO-11, SAPO-34 etc. are mentioned, You may use 2 or more types together. Among these, SAPO-34 is preferable.

The average particle diameter of SAPO is preferably 1/5 to 50 times, more preferably 1/3 to 30 times the average particle diameter of CHA. This is because the pore diameter of the honeycomb unit can be adjusted.
The average particle size of SAPO is the average particle size of primary particles measured using a scanning electron microscope (SEM).

For example, when the average particle diameter of CHA is 0.1 μm, the average particle diameter of SAPO is preferably 0.1 to 3.0 μm, and when the average particle diameter of CHA is 1.5 μm, the average SAPO The particle diameter is desirably 0.5 to 5.0 μm.

The specific surface area of SAPO is preferably 200 to 500 m ² / g and more preferably 220 to 450 m ² / g from the viewpoint of the crystal structure.

The SAPO content in the honeycomb unit is desirably 5 to 25% by volume, and more desirably 8 to 20% by volume. If the SAPO content is less than 5% by volume, the amount of CHA is too much, so that the honeycomb unit is likely to be damaged by absorption / desorption or thermal stress. On the other hand, if the SAPO content exceeds 25% by volume, the CHA content decreases and the NOx purification performance decreases. Further, the honeycomb unit is liable to be damaged by absorption and dehydration.

In the honeycomb catalyst of the present invention, the volume ratio (CHA: SAPO) of the first zeolite and the second zeolite is 75:25 to 90:10, desirably 78:22 to 88:12, Desirably, it is 80: 20-85: 15. By setting the volume ratio of CHA and SAPO to 75:25 to 90:10, the NOx purification performance is excellent, and damage to the honeycomb unit (damage due to water absorption / dehydration and thermal stress) during use of the exhaust gas purification device is suppressed. The honeycomb catalyst can be made.

In the honeycomb catalyst of the present invention, the honeycomb unit may contain zeolite other than CHA and SAPO within a range not impairing the effects of the present invention.

In the honeycomb catalyst of the present invention, it is desirable that the first zeolite (CHA) and / or the second zeolite (SAPO) is ion-exchanged with copper ions, and at least the first zeolite is ion-exchanged with copper ions. More desirably, the first zeolite and the second zeolite are more preferably ion-exchanged with copper ions. In this case, the honeycomb unit preferably contains copper ions at 5.5 to 7.5 g / L and more preferably 6.0 to 7.5 g / L per apparent volume of the honeycomb unit. Since the NOx purification performance when the exhaust gas temperature is low can be increased and the decrease in the NOx purification performance due to ammonia oxidation at a high temperature can be prevented, high NOx purification performance is exhibited over the entire temperature range.

In the honeycomb catalyst of the present invention, the honeycomb unit preferably contains 150 to 250 g / L, more preferably 180 to 230 g / L of the first zeolite (CHA) per apparent volume of the honeycomb unit. Since the NOx purification performance when the exhaust gas temperature is low can be increased and the decrease in the NOx purification performance due to ammonia oxidation at a high temperature can be prevented, high NOx purification performance is exhibited over the entire temperature range.

In the honeycomb catalyst of the present invention, the inorganic binder contained in the honeycomb unit is not particularly limited, but is contained in alumina sol, silica sol, titania sol, water glass, sepiolite, attapulgite, boehmite, etc. from the viewpoint of maintaining strength as a honeycomb catalyst. The solid content is suitable, and two or more kinds may be used in combination.

The content of the inorganic binder in the honeycomb unit is desirably 3 to 30% by volume, and more desirably 5 to 20% by volume. When the content of the inorganic binder is less than 3% by volume, the strength of the honeycomb unit is lowered. On the other hand, when the content of the inorganic binder exceeds 30% by volume, the content of zeolite in the honeycomb unit is lowered, and the NOx purification performance is lowered.

In the honeycomb catalyst of the present invention, the honeycomb unit preferably further includes at least one selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances, and three-dimensional needle-like substances in order to improve strength. .

The inorganic fiber contained in the honeycomb unit is desirably composed of one or more selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, potassium titanate, and aluminum borate. The scaly substance contained in the honeycomb unit is preferably made of one or more selected from the group consisting of glass, muscovite, alumina, and silica. The tetrapot-like substance contained in the honeycomb unit is preferably made of zinc oxide. The three-dimensional acicular substance contained in the honeycomb unit is desirably composed of one or more selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, potassium titanate, aluminum borate and boehmite. This is because all of them have high heat resistance, and even when used as a catalyst carrier in an SCR system, there is no melting damage and the effect as a reinforcing material can be maintained.

The aspect ratio of the inorganic fibers contained in the honeycomb unit is desirably 2 to 300, more desirably 5 to 200, and further desirably 10 to 100. When the aspect ratio of the inorganic fiber is less than 2, the effect of improving the strength of the honeycomb unit is reduced. On the other hand, when the aspect ratio of the inorganic fibers exceeds 300, clogging or the like occurs in the mold when the honeycomb unit is extruded, or the inorganic fibers break and the effect of improving the strength of the honeycomb unit is reduced. To do.

The scaly substance means a flat substance, desirably having a thickness of 0.2 to 5.0 μm, desirably having a maximum length of 10 to 160 μm, and having a ratio of the maximum length to the thickness of 3 It is desirable to be ~ 250.

The tetrapot-like substance means a substance in which the needle-like portion extends three-dimensionally. The average needle-like length of the needle-like portion is desirably 5 to 30 μm, and the average diameter of the needle-like portion is 0.5. It is desirable that it is -5.0 micrometers.

The three-dimensional acicular substance means a substance in which the acicular parts are bonded by an inorganic compound such as glass near the center of each acicular part, and the average acicular length of the acicular parts is 5 to 30 μm. It is desirable that the average diameter of the needle-shaped part is 0.5 to 5.0 μm.

The three-dimensional acicular substance may have a plurality of acicular portions that are three-dimensionally connected, and preferably has a diameter of 0.1 to 5.0 μm and a length of 0.3 to 5.0 μm. 30.0 μm is desirable, and the ratio of length to diameter is desirably 1.4 to 50.0.

The content of inorganic fiber, scale-like substance, tetrapot-like substance and three-dimensional needle-like substance in the honeycomb unit is preferably 3 to 50% by volume, more preferably 3 to 30% by volume. More desirably, it is ˜20% by volume. When the content is less than 3% by volume, the effect of improving the strength of the honeycomb unit is reduced. On the other hand, when the content exceeds 50% by volume, the content of zeolite in the honeycomb unit decreases, and the NOx purification performance decreases.

In the honeycomb catalyst of the present invention, the honeycomb unit may further contain inorganic particles in order to adjust the pore diameter of the honeycomb unit.

The inorganic particles contained in the honeycomb unit are not particularly limited, and examples thereof include particles such as alumina, titania, zirconia, silica, ceria, and magnesia. Two or more of these may be used in combination. The inorganic particles are preferably one or more particles selected from the group consisting of alumina, titania and zirconia, and more preferably any one of alumina, titania and zirconia.

The average particle size of the inorganic particles is desirably 0.1 to 5.0 μm, more desirably 0.3 to 4.5 μm, and further desirably 0.5 to 4.0 μm. When the average particle size of the inorganic particles is 0.1 to 5.0 μm, the pore size of the honeycomb unit can be adjusted.
The average particle size of the inorganic particles is the particle size (Dv50) at an integrated value of 50% in the particle size distribution (volume basis) obtained by the laser diffraction / scattering method.

The content of inorganic particles in the honeycomb unit is preferably 5 to 20% by volume, and more preferably 5 to 15% by volume.

In the honeycomb catalyst of the present invention, the porosity of the honeycomb unit is preferably 40 to 70%. When the porosity of the honeycomb unit is less than 40%, the exhaust gas hardly enters the partition walls of the honeycomb unit, and the zeolite is not effectively used for the purification of NOx. On the other hand, when the porosity of the honeycomb unit exceeds 70%, the strength of the honeycomb unit becomes insufficient.

The porosity of the honeycomb unit can be measured by Archimedes method.

In the honeycomb catalyst of the present invention, the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit is preferably 50 to 75%. If the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit is less than 50%, zeolite is not effectively used for NOx purification. On the other hand, when the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit exceeds 75%, the strength of the honeycomb unit becomes insufficient.

In the honeycomb catalyst of the present invention, it is desirable that the density of through-holes in a cross section perpendicular to the longitudinal direction of the honeycomb unit is 31 to 155 holes / cm ² . If the density of the through-holes having a cross section perpendicular to the longitudinal direction of the honeycomb unit is less than 31 / cm ² , it becomes difficult for the zeolite and the exhaust gas to come into contact with each other, and the NOx purification performance decreases. On the other hand, when the density of the through holes in the cross section perpendicular to the longitudinal direction of the honeycomb unit exceeds 155 holes / cm ² , the pressure loss of the honeycomb catalyst increases.

In the honeycomb catalyst of the present invention, the thickness of the partition walls of the honeycomb unit is desirably 0.1 to 0.4 mm, and more desirably 0.1 to 0.3 mm. When the thickness of the partition walls of the honeycomb unit is less than 0.1 mm, the strength of the honeycomb unit decreases. On the other hand, when the thickness of the partition wall of the honeycomb unit exceeds 0.4 mm, the exhaust gas hardly enters the inside of the partition wall of the honeycomb unit, and the zeolite is not effectively used for purification of NOx.

In the honeycomb catalyst of the present invention, when the outer peripheral coat layer is formed on the honeycomb unit, the thickness of the outer peripheral coat layer is preferably 0.1 to 2.0 mm. When the thickness of the outer peripheral coat layer is less than 0.1 mm, the effect of improving the strength of the honeycomb catalyst becomes insufficient. On the other hand, when the thickness of the outer peripheral coat layer exceeds 2.0 mm, the content of zeolite per unit volume of the honeycomb catalyst decreases, and the NOx purification performance decreases.

The shape of the honeycomb catalyst of the present invention is not limited to a cylindrical shape, and examples thereof include a prismatic shape, an elliptical cylindrical shape, a long cylindrical shape, and a rounded chamfered prismatic shape (for example, a rounded chamfered triangular prism shape).

In the honeycomb catalyst of the present invention, the shape of the through hole is not limited to a quadrangular prism shape, and examples thereof include a triangular prism shape and a hexagonal prism shape.

Next, an example of a method for manufacturing the honeycomb catalyst 10 shown in FIG. 1 will be described.
First, it contains a first zeolite, a second zeolite, and an inorganic binder, and if necessary, one or more selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances and three-dimensional needle-like substances Further, a raw material paste containing the resultant is extruded to produce a cylindrical honeycomb formed body in which a plurality of through holes are arranged in parallel in the longitudinal direction with a partition wall therebetween.

The inorganic binder contained in the raw material paste is not particularly limited, but is added as alumina sol, silica sol, titania sol, water glass, sepiolite, attapulgite, boehmite, etc., and two or more kinds may be used in combination.

Moreover, you may add an organic binder, a dispersion medium, a shaping | molding adjuvant, etc. to a raw material paste suitably as needed.

Although it does not specifically limit as an organic binder, Methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyethyleneglycol, a phenol resin, an epoxy resin etc. are mentioned, You may use 2 or more types together. The addition amount of the organic binder is desirably 1 to 10% with respect to the total mass of zeolite, inorganic particles, inorganic binder, inorganic fiber, scale-like substance, tetrapot-like substance, and three-dimensional acicular substance. .

Although it does not specifically limit as a dispersion medium, Alcohol, such as water, organic solvents, such as benzene, methanol, etc. are mentioned, You may use 2 or more types together.

Although it does not specifically limit as a shaping | molding adjuvant, Ethylene glycol, dextrin, a fatty acid, fatty acid soap, a polyalcohol etc. are mentioned, You may use together 2 or more types.

Furthermore, a pore former may be added to the raw material paste as necessary.
Although it does not specifically limit as a pore making material, A polystyrene particle, an acrylic particle, starch, etc. are mentioned, You may use 2 or more types together. Of these, polystyrene particles are desirable.

By controlling the particle diameters of the CHA and the pore former, the pore diameter distribution of the partition walls can be controlled within a predetermined range.
For example, when the average particle diameter of CHA is 0.1 μm, by adding 10 to 30% of the pore former having an average particle diameter of 0.1 to 3 μm to the CHA volume addition amount, The pore diameter can be 0.05 to 0.2 μm. In addition, when the average particle diameter of CHA is 1.2 μm, it is not necessary to add a pore former.

Even when no pore former is added, the pore size distribution of the partition walls can be controlled within a predetermined range by controlling the particle sizes of CHA and SAPO.

When preparing the raw material paste, it is desirable to mix and knead, and it may be mixed using a mixer, an attritor or the like, or may be kneaded using a kneader or the like.

Next, the honeycomb formed body is dried by using a dryer such as a microwave dryer, a hot air dryer, a dielectric dryer, a vacuum dryer, a vacuum dryer, or a freeze dryer to produce a honeycomb dried body.

Further, the honeycomb dried body is degreased to produce a honeycomb degreased body. The degreasing conditions can be appropriately selected depending on the type and amount of organic matter contained in the dried honeycomb body, but it is desirable that the degreasing conditions be 200 to 500 ° C. for 2 to 6 hours.

Next, the honeycomb degreased body is fired to produce a columnar honeycomb unit 11. The firing temperature is desirably 600 to 1000 ° C, and more desirably 600 to 800 ° C. When the firing temperature is less than 600 ° C., the sintering does not proceed and the strength of the honeycomb unit 11 is lowered. On the other hand, if the calcination temperature exceeds 1000 ° C., the sintering proceeds too much and the reaction sites of the zeolite decrease.

Next, the outer peripheral coat layer paste is applied to the outer peripheral surface excluding both end surfaces of the columnar honeycomb unit 11.

Although it does not specifically limit as a paste for outer periphery coating layers, The mixture of an inorganic binder and an inorganic particle, the mixture of an inorganic binder and an inorganic fiber, the mixture of an inorganic binder, an inorganic particle, and an inorganic fiber etc. are mentioned.

Although the inorganic binder contained in the outer periphery coating layer paste is not particularly limited, it is added as silica sol, alumina sol or the like, and two or more kinds may be used in combination. Among these, it is desirable to add as silica sol.

The inorganic particles contained in the outer coat layer paste are not particularly limited, but oxide particles such as zeolite, eucryptite, alumina and silica, carbide particles such as silicon carbide, and nitride particles such as silicon nitride and boron nitride. Etc., and two or more of them may be used in combination. Among them, eucryptite particles having a thermal expansion coefficient close to that of the honeycomb unit are desirable.

Although it does not specifically limit as an inorganic fiber contained in the paste for outer periphery coating layers, A silica alumina fiber, a mullite fiber, an alumina fiber, a silica fiber, etc. are mentioned, You may use 2 or more types together. Among these, alumina fibers are preferable.

The outer periphery coating layer paste may further contain an organic binder.

Although it does not specifically limit as an organic binder contained in the paste for outer periphery coating layers, Polyvinyl alcohol, methylcellulose, ethylcellulose, carboxymethylcellulose, etc. are mentioned, You may use 2 or more types together.

The outer periphery coating layer paste may further include balloons, pore formers, and the like, which are fine hollow spheres of oxide ceramics.

The balloon contained in the outer peripheral coat layer paste is not particularly limited, and examples thereof include alumina balloons, glass micro balloons, shirasu balloons, fly ash balloons, mullite balloons and the like, and two or more kinds may be used in combination. Among these, an alumina balloon is preferable.

The pore former contained in the outer periphery coat layer paste is not particularly limited, and examples thereof include spherical acrylic particles and graphite, and two or more kinds may be used in combination.

Next, the honeycomb unit 11 to which the outer peripheral coat layer paste is applied is dried and solidified to produce a columnar honeycomb catalyst 10. At this time, when the outer peripheral coat layer paste contains an organic binder, it is desirable to degrease. The degreasing conditions can be appropriately selected depending on the kind and amount of the organic substance, but it is desirable that the degreasing conditions be 500 ° C. for 1 hour.

Note that the zeolite may be ion-exchanged by immersing the honeycomb unit 11 or the honeycomb catalyst 10 in an aqueous solution containing copper ions. Moreover, you may use the raw material paste containing the zeolite ion-exchanged with copper ion.

FIG. 2 shows an example of the exhaust gas purifying apparatus of the present invention. The exhaust gas purification apparatus 100 shown in FIG. 2 can be manufactured by canning the metal container (shell) 30 in a state where the holding sealing material 20 is disposed on the outer peripheral portion of the honeycomb catalyst 10. Further, in the exhaust gas purifying device 100, in the pipe (not shown) on the upstream side of the honeycomb catalyst 10 with respect to the direction in which the exhaust gas (in FIG. Injecting means (not shown) such as an injection nozzle for injecting ammonia or a compound that decomposes to generate ammonia is provided. As a result, ammonia is added to the exhaust gas flowing through the pipe, so that NOx contained in the exhaust gas is reduced by the zeolite contained in the honeycomb unit 11.

The compound that decomposes to generate ammonia is not particularly limited as long as it can be hydrolyzed in the pipe to generate ammonia, but urea water is preferable because of excellent storage stability.

The urea water is heated by the exhaust gas in the pipe and hydrolyzes to generate ammonia.

FIG. 3 shows another example of the honeycomb catalyst of the present invention. A honeycomb catalyst 10 ′ shown in FIG. 3 has a plurality of honeycomb units 11 ′ (see FIG. 4) in which a plurality of through-holes 11 a are arranged in parallel in the longitudinal direction with a partition wall 11 b interposed therebetween, and are bonded via an adhesive layer 13. Except for this, the configuration is the same as that of the honeycomb catalyst 10.

The cross-sectional area of the cross section perpendicular to the longitudinal direction of the honeycomb unit 11 ′ is desirably 10 to ²⁰⁰ cm ² . When the cross-sectional area is less than 10 cm ² , the pressure loss of the honeycomb catalyst 10 ′ increases. On the other hand, when the cross-sectional area exceeds 200 cm ² , it is difficult to bond the honeycomb units 11 ′.

The honeycomb unit 11 ′ has the same configuration as the honeycomb unit 11 except for the cross-sectional area of the cross section perpendicular to the longitudinal direction.

The thickness of the adhesive layer 13 is desirably 0.1 to 3.0 mm. When the thickness of the adhesive layer 13 is less than 0.1 mm, the adhesive strength of the honeycomb unit 11 ′ becomes insufficient. On the other hand, when the thickness of the adhesive layer 13 exceeds 3.0 mm, the pressure loss of the honeycomb catalyst 10 ′ increases or cracks occur in the adhesive layer.

Next, an example of a method for manufacturing the honeycomb catalyst 10 ′ shown in FIG. 3 will be described.
First, in the same manner as the honeycomb unit 11 constituting the honeycomb catalyst 10, a fan-shaped honeycomb unit 11 ′ is manufactured. Next, an adhesive layer paste is applied to the outer peripheral surface excluding the arc side of the honeycomb unit 11 ′, the honeycomb unit 11 ′ is adhered, and dried and solidified to produce an aggregate of the honeycomb units 11 ′.

Although it does not specifically limit as a paste for contact bonding layers, The mixture of an inorganic binder and an inorganic particle, the mixture of an inorganic binder and an inorganic fiber, the mixture of an inorganic binder, an inorganic particle, and an inorganic fiber etc. are mentioned.

The inorganic binder contained in the adhesive layer paste is not particularly limited, but is added as silica sol, alumina sol or the like, and two or more kinds may be used in combination. Among these, it is desirable to add as silica sol.

The inorganic particles contained in the adhesive layer paste are not particularly limited, but oxide particles such as zeolite, eucryptite, alumina and silica, carbide particles such as silicon carbide, nitride particles such as silicon nitride and boron nitride, etc. And two or more of them may be used in combination. Among them, eucryptite particles having a thermal expansion coefficient close to that of the honeycomb unit are desirable.

Although it does not specifically limit as an inorganic fiber contained in the paste for contact bonding layers, A silica alumina fiber, a mullite fiber, an alumina fiber, a silica fiber etc. are mentioned, You may use 2 or more types together. Among these, alumina fibers are preferable.

The adhesive layer paste may contain an organic binder.

Although it does not specifically limit as an organic binder contained in the paste for contact bonding layers, Polyvinyl alcohol, methylcellulose, ethylcellulose, carboxymethylcellulose etc. are mentioned, You may use 2 or more types together.

The adhesive layer paste may further include balloons, pore formers, and the like, which are fine hollow spheres of oxide ceramics.

Although it does not specifically limit as a balloon contained in the paste for contact bonding layers, An alumina balloon, a glass micro balloon, a shirasu balloon, a fly ash balloon, a mullite balloon etc. are mentioned, You may use 2 or more types together. Among these, an alumina balloon is preferable.

The pore former contained in the adhesive layer paste is not particularly limited, and examples thereof include spherical acrylic particles and graphite, and two or more kinds may be used in combination.

Next, in order to increase the roundness, the aggregate of the honeycomb units 11 ′ is subjected to cutting and polishing as necessary to produce the aggregate of the cylindrical honeycomb units 11 ′.

Next, the outer peripheral coat layer paste is applied to the outer peripheral surface excluding both end surfaces of the aggregate of the cylindrical honeycomb units 11 ′.

The outer periphery coating layer paste may be the same as or different from the adhesive layer paste.

Next, a columnar honeycomb catalyst 10 ′ is manufactured by drying and solidifying the aggregate of columnar honeycomb units 11 ′ to which the outer periphery coating layer paste has been applied. At this time, when the adhesive for the adhesive layer and / or the paste for the outer peripheral coat layer contains an organic binder, it is desirable to degrease. The degreasing conditions can be appropriately selected depending on the kind and amount of the organic substance, but it is desirable that the degreasing conditions be 500 ° C. for 1 hour.

The honeycomb catalyst 10 ′ is configured by bonding four honeycomb units 11 ′ via the adhesive layer 13, but the number of honeycomb units constituting the honeycomb catalyst is not particularly limited. For example, a columnar honeycomb catalyst may be configured by adhering 16 square columnar honeycomb units via an adhesive layer.

The honeycomb catalysts 10 and 10 ′ may not have the outer peripheral coat layer 12 formed thereon.

As described above, in the honeycomb catalyst of the present invention, the NOx purification performance can be improved by using a honeycomb unit that uses CHA, which is the first zeolite, as the main raw material. Further, by mixing CHA and SAPO, which is the second zeolite, to form a honeycomb unit, the water absorption and dehydration stress of the entire honeycomb unit can be relaxed. Specifically, by setting the volume ratio of CHA and SAPO to 75:25 to 90:10, the NOx purification performance is excellent, and the honeycomb unit is damaged during use of the exhaust gas purification device (due to water absorption / dehydration and thermal stress). A honeycomb catalyst capable of suppressing (breakage) can be obtained.

Examples in which the present invention is disclosed more specifically are shown below. In addition, this invention is not limited only to this Example.

[Example 1]
27% by mass of CHA having an average particle size of 0.1 μm as the first zeolite, 8% by mass of SAPO having an average particle size of 3.0 μm as the second zeolite, 7% by mass of boehmite as the inorganic binder, average fiber diameter Is 7% by mass of glass fiber having an average fiber length of 100 μm, 7% by mass of polystyrene particles having an average particle diameter of 0.8 μm as a pore former, 6% by mass of methylcellulose, and fatty acid soap as a molding aid. 4% by mass and 34% by mass of ion-exchanged water were mixed and kneaded to prepare a raw material paste 1. As the first zeolite, a specific gravity of 2.02, a composition ratio of Si / Al: 32, a specific surface area of 600 m ² / g, CHA ion-exchanged with copper ions is used, and a specific gravity of 2 is used as the second zeolite. 0.53, composition ratio Si / (Si + Al + P): 0.17, specific surface area 223 m ² / g, SAPO ion-exchanged with copper ions was used.
In Example 1, the volume ratio (CHA: SAPO) of the first zeolite and the second zeolite is 80:20.

Next, the raw material paste 1 was extrusion-molded using an extruder to produce a regular quadrangular prism-shaped honeycomb formed body. Then, using a vacuum microwave dryer, the honeycomb formed body was dried at an output of 4.5 kW and a reduced pressure of 6.7 kPa for 7 minutes, and then degreased and fired at 700 ° C. for 2 hours to obtain a honeycomb fired body (honeycomb unit 11 ′ ) Was produced. The honeycomb unit 11 ′ was a regular quadrangular prism shape with a side of 38 mm and a length of 150 mm, the density of the through holes 11 a was 124 / cm ² , and the thickness of the partition walls 11 b was 0.20 mm.
Further, the honeycomb unit 11 ′ contains 254 g / L of the first zeolite and the second zeolite and 9.4 g / L of copper ions per apparent volume of the honeycomb unit 11 ′.

[Comparative Example 1]
A honeycomb unit 11 ′ was produced in the same manner as in Example 1 except that the volume ratio (CHA: SAPO) of the first zeolite and the second zeolite was changed to 70:30.

[Comparative Example 2]
A honeycomb unit 11 ′ was produced in the same manner as in Example 1 except that the volume ratio (CHA: SAPO) of the first zeolite and the second zeolite was changed to 100: 0. That is, in Comparative Example 2, the second zeolite (SAPO) was not used.

[Measurement of NOx purification rate]
A cylindrical test piece having a diameter of 1 inch and a length of 3 inches was cut out from the honeycomb unit manufactured in Example 1, Comparative Example 1 and Comparative Example 2 using a diamond cutter. While passing a simulated gas at 200 ° C. or 525 ° C. at a space velocity (SV) of 40000 / hr (200 ° C.) and 100000 / hr (525 ° C.) through these test pieces, a catalyst evaluation apparatus (SIGU- manufactured by Horiba, Ltd.) was used. 2000 / MEXA-6000FT) is used to measure the outflow amount of NOx flowing out from the sample, and the formula (NOx inflow amount−NOx outflow amount) / (NOx inflow amount) × 100
The NOx purification rate [%] expressed by The calculation results are shown in Table 1. The components of the simulated gas are 260 ppm nitrogen monoxide, 90 ppm nitrogen dioxide, 350 ppm ammonia (200 ° C.), 315 ppm nitrogen monoxide, 35 ppm nitrogen dioxide, 385 ppm ammonia (525 ° C.), 10% oxygen, 5% carbon dioxide, Water 5%, nitrogen balance.

From Table 1, it can be seen that in any of the honeycomb units, the NOx purification rate at 200 ° C. is as high as about 95%, and the NOx purification rate at 525 ° C. is as high as about 80%.

[Measurement of thermal expansion coefficient]
From the honeycomb units manufactured in Example 1, Comparative Example 1 and Comparative Example 2, a square prism-shaped measurement sample having a side of 5 mm and a height of 25 mm was cut out using a diamond cutter. Thereafter, the sample was dried at 200 ° C. for 2 hours, the weight was measured, and the sample was allowed to stand in a water vapor atmosphere until the water absorption rate of the measurement sample reached 10%.
With respect to these measurement samples, the temperature was increased from 50 ° C. to 700 ° C. at a temperature increase rate of 10 ° C./min, and then decreased to 50 ° C. at 10 ° C./min. The thermal expansion coefficient (CTE) in the radial direction of each honeycomb unit was measured using a thermal dilatometer (manufactured by BRUKER, NETZSCH DIL402C). The measurement was performed in an atmosphere with a He flow rate of 100 ml / min. A graph of the measurement results is shown in FIG.

FIG. 5 shows that in Example 1 where the ratio of SAPO to the total amount of CHA and SAPO is 20% by volume, the rate of change of the thermal expansion coefficient is small in the entire temperature range. On the other hand, in Comparative Example 1 in which the ratio of SAPO to the total amount of CHA and SAPO is 30% by volume and Comparative Example 2 in which no SAPO is contained, the rate of change of the thermal expansion coefficient in the vicinity of 80 to 100 ° C. is large. . Therefore, it is considered that the breakage of the honeycomb unit due to absorption and dehydration can be suppressed by setting the volume ratio of CHA and SAPO to an appropriate range.

[Thermal cycle test]
The honeycomb catalyst produced in Example 1, Comparative Example 1 and Comparative Example 2 was heated to 700 ° C., and then cooled to 200 ° C., and one cycle was performed, and a thermal cycle test was repeated 5 times.

As a result of the thermal cycle test, in Example 1 in which the proportion of SAPO to the total amount of CHA and SAPO was 20% by volume and in Comparative Example 1 in which the proportion of SAPO was 30% by volume, the honeycomb unit was not damaged. In Comparative Example 2 containing no SAPO, the honeycomb unit was damaged. Therefore, it is considered that the honeycomb unit can be prevented from being damaged by thermal stress by forming a honeycomb unit by mixing CHA and SAPO.

From the above, it is considered that the honeycomb catalyst of the present invention is excellent in NOx purification performance and can suppress damage to the honeycomb unit (damage due to water absorption / dehydration and thermal stress) during use of the exhaust gas purification apparatus.

The honeycomb catalyst of the present invention includes a honeycomb unit in which a plurality of through holes are arranged in parallel in the longitudinal direction with a partition wall therebetween, the honeycomb unit includes a first zeolite, a second zeolite, and an inorganic binder, The zeolite 1 is an aluminosilicate having a CHA structure, the composition ratio Si / Al is 15 to 50, the second zeolite is a silicoaluminophosphate, and the composition ratio Si / (Si + Al + P) is 0. 1 to 0.25, and the volume ratio of the first zeolite to the second zeolite (first zeolite: second zeolite) is 75:25 to 90:10 as an essential constituent requirement Yes. The exhaust gas purification apparatus of the present invention is provided with the honeycomb catalyst of the present invention as an essential constituent requirement.
The essential constitutional requirements include various constitutions detailed in the detailed description of the present invention (for example, the constitution of the first zeolite, the constitution of the second zeolite, the constitution of the inorganic binder, the constitution of the honeycomb unit, the constitution of the honeycomb catalyst, Desired effects can be obtained by appropriately combining the manufacturing conditions, the configuration of the exhaust gas purification device, and the like.

10, 10 'Honeycomb catalyst 11, 11' Honeycomb unit 11a Through-hole 11b Partition 12 Outer peripheral coat layer 13 Adhesive layer 20 Holding sealing material 30 Metal container 100 Exhaust gas purification device G Exhaust gas

Claims (8)

A honeycomb catalyst including a honeycomb unit in which a plurality of through holes are arranged in parallel in a longitudinal direction with a partition wall therebetween,
The honeycomb unit includes a first zeolite, a second zeolite, and an inorganic binder,
The first zeolite is an aluminosilicate having a CHA structure, and the composition ratio Si / Al is 15 to 50,
The second zeolite is silicoaluminophosphate, the composition ratio Si / (Si + Al + P) is 0.1-0.25,
A honeycomb catalyst, wherein a volume ratio of the first zeolite and the second zeolite (first zeolite: second zeolite) is 75:25 to 90:10. The honeycomb catalyst according to claim 1, wherein an average particle size of the first zeolite is 0.1 to 2.0 µm. The honeycomb catalyst according to claim 1 or 2, wherein the average particle diameter of the second zeolite is 1/5 to 50 times the average particle diameter of the first zeolite. The honeycomb catalyst according to any one of claims 1 to 3, wherein the first zeolite and / or the second zeolite are ion-exchanged with copper ions. The honeycomb catalyst according to claim 4, wherein the honeycomb unit contains 5.5 to 7.5 g / L of the copper ions per apparent volume of the honeycomb unit. The honeycomb catalyst according to any one of claims 1 to 5, wherein the honeycomb unit contains the first zeolite in an amount of 150 to 250 g / L per apparent volume of the honeycomb unit. The honeycomb catalyst according to any one of claims 1 to 6, wherein the honeycomb unit further includes one or more selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances, and three-dimensional needle-like substances. An exhaust gas purification apparatus comprising the honeycomb catalyst according to any one of claims 1 to 7.